1. Field of the Invention
The present invention relates to an active vibratory noise control apparatus.
2. Description of the Related Art
In the related art, active vibratory noise control apparatuses for adaptively reducing vibratory noise in a passenger compartment of a vehicle in accordance with a control signal having the frequency of vibratory noise of an engine are proposed in, for example, Japanese Patents No. 3843082 ([0012], [0013], [0014], [0016]) and No. 4074612 ([0012], [0015], [0016], [0169]).
In the active vibratory noise control apparatus proposed in Japanese Patent No. 3843082, a basic signal generating means generates basic signals (a basic sine wave signal and a basic cosine wave signal) having frequencies that are based on the frequency of vibratory noise generated from a vibratory noise source, and a first adaptive notch filter generates a first control signal based on the generated basic cosine wave signal. Further, a second adaptive notch filter generates a second control signal based on the generated basic sine wave signal. Vibratory-noise canceling sound is generated from a speaker based on a sum signal representing the sum of the first control signal and the second control signal to cancel the vibratory noise.
In the cancellation of vibratory noise, an error signal that is based on the difference between the vibratory noise and the vibratory-noise canceling sound is detected using a microphone, and a signal produced by subtracting the product of a sine correction value based on the sine value of the phase characteristics in the signal transfer characteristics at the frequencies of the basic signals from the speaker to the microphone and the basic sine wave signal from the product of a cosine correction value based on the cosine value of the phase characteristics and the basic cosine wave signal is generated as a first reference signal. Further, a signal produced by summing the product of the sine correction value and the basic cosine wave signal and the product of the cosine correction value and the basic sine wave signal is generated as a second reference signal. A filter coefficient updating means sequentially updates the filter coefficients of the first and second adaptive notch filters so that the error signal can be minimized based on the error signal and the first and second reference signals. Thus, the vibratory noise is canceled by the vibratory-noise canceling sound output from the speaker.
The active vibratory noise control apparatus proposed in Japanese Patent No. 4074612 has a specific and simple configuration of a basic signal generating means and a reference signal generating means. In the apparatus, the basic signal generating means includes a waveform data storage means for storing, as waveform data, instantaneous value data obtained at individual segment positions determined by dividing the sine wave of one period by a predetermined number. Waveform data is read in sequence from the waveform data storage means for each sampling to generate a basic sine wave signal, and waveform data is read in sequence from addresses of the waveform data storage means, which are shifted by a quarter period with respect to the addresses at which the basic sine wave signal is read, to generate a basic cosine wave signal.
Further, the reference signal generating means includes a correction data storage means for storing, when correcting the basic sine wave signal and the basic cosine wave signal based on correction values indicating the phase characteristics in the transfer characteristics from the speaker to the microphone with respect to the frequencies of the basic signals and when outputting the corrected signals as reference signals, the correction values with respect to the frequencies of the basic signals, and is configured to generate a reference signal by referring to the frequencies of the basic signals, reading the correction values from the correction data storage means, and reading waveform data from the addresses that are shifted by the correction values with respect to the addresses at which the waveform data is read from the waveform data storage means.
In the technique disclosed in Japanese Patent No. 3843082, the correction values include a sine correction value that is based on a phase-delayed sine value and a cosine correction value that is based on a phase-delayed cosine value in the signal transfer characteristics of vibratory sound from the speaker to the microphone, which correspond to the frequencies of the basic signals, and are stored in advance in the storage means in correspondence with the frequencies of the basic signals. The correction values are read in correspondence with the frequencies of the basic signals, and the read cosine correction value and sine correction value are multiplied by the basic cosine wave signal and the basic sine wave signal. The multiplication results are summed to obtain a reference signal. Thus, the amount of computation required to obtain a reference signal is significantly smaller than that required when a FIR filter is used, and an active vibratory noise control apparatus can be manufactured inexpensively.
In the technique disclosed in Japanese Patent No. 4074612, address shift values that are based on the phase characteristics in the signal transfer characteristics from the speaker to the microphone are stored in advance in the correction data storage means in accordance with the frequencies of basic signals, and waveform data read from an address that is shifted by an address shift value read from the correction data storage means with respect to address data for reading a basic cosine wave signal and a basic sine wave signal from the waveform data storage means by referring to the frequencies of the basic signals is used as first and second reference signals. Thus, the signal transfer characteristics can be optimally modeled, and first and second reference signals can be obtained with a smaller amount of computation than that required when a FIR filter is used. In addition, vibratory noise can be canceled with sufficient convergence.
As described above, Japanese Patents No. 3843082 and No. 4074612 describe that with the use of an adaptive FIR filter instead of an adaptive notch filter, a large computational load is required to generate a reference signal and a processor with high computation performance, such as a digital signal processor, is required.